Communication node, and token issuing method and token-ring communication method in ring communication system

ABSTRACT

A communication node includes a token-start-right acquisition processor that issues a token-start-right acquisition frame containing specific information, determines a priority based on predetermined reference using specific information for other communication node and the specific information for the own communication node upon reception of a token-start-right acquisition frame from the other communication node, issues the token-start-right acquisition frame at a predetermined time interval when the own communication node has a higher priority than the other communication node, and stops issuing the token-start-right acquisition frame when the own communication node has a lower priority than the other communication node, to forward the token-start-right acquisition frame of the other communication node, and also includes a token start processor that passes the token frame to the ring upon reception of the token-start-right acquisition frame which is issued by the token-start-right acquisition processor and circulates around the ring.

The present application is a Continuation of U.S. application Ser. No.12/297,830, filed Oct. 20, 2008, which claims priority to PCTInternational Application No. PCT/JP2006/312743, filed Jun. 26, 2006.The entire disclosures of the prior applications are hereby incorporatedby reference.

TECHNICAL FIELD

The present invention relates to a communication node used in anEthernet (registered trademark)-base ring communication systemcommunicating an Ethernet (registered trademark) in the shape of a ring,a token issuing method and a token-ring communication method in the ringcommunication system that allows masterless token ring communication inthe communication system.

BACKGROUND ART

There is conventionally known a topology in which a network isconstructed by connecting between communication terminals (hereinafter,“communication nodes”) using FDDI (Fiber-Distributed Data Interface)(for example, Nonpatent literature 1). In the FDDI, generally, a networkis constructed so that communication nodes are connected in a ring. Thenetwork using the FDDI is formed of a dual-loop structure having a firstloop in which data is transmitted in a normal state, and a second loopwhich is configured so as to enable communication using a normalportion, when abnormality such as disconnection of a cable forming thefirst loop and failure in a communication node occurs, by performingloop-back so as to disconnect an abnormal portion from the network.

Further, the FDDI employs a token passing system that provides controlsso that collisions of data transmitted between communication nodesconnected to the network do not occur by using data for the right totransmit called a token. The token passing system is implemented in sucha manner that a token is passed around the first loop, and acommunication node wishing to transmit data takes the token, passes datainstead that the communication node itself wishes to transmit, andreleases the token again to the network when the transmission isfinished, so that only one terminal can use the cable at a time.

Nonpatent literature 1: “Details of FDDI Technology-Construction of 100Mbps LAN-” written by Karl F. Pieper, William J. Cronin Jr., and WendyH. Michael, translated and supervised by Naoki Mizutame, first edition,published by Kyoritsu Shuppan Co., Aug. 30, 1993, p. 67 to 73.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

Currently, however, a configuration in which a network is constructed byconnecting between communication nodes using Ethernet (registeredtrademark) is widely used. The Ethernet (registered trademark) employs aCSMA/CD (Carrier Sense Multiple Access/Collision Detection) system thatgets communication right while avoiding collisions, when thecommunication node connected to the Ethernet (registered trademark)transmits data, and propagates the data to all the connectedcommunication nodes. To function the system, a connection configurationof the communication nodes in the Ethernet (registered trademark)includes two topologies such as a bus topology constructed by extendingbranch cables, from one cable which is a mainline, provided atappropriate intervals to arrange a plurality of communication nodesthereat, and a star topology constructed by radially arranging aplurality of communication nodes around one control unit (hub).

However, the Ethernet (registered trademark) is a system in whichterminal devices connected to the network perform termination (discard)of Ethernet (registered trademark) frames, and thus this system has aproblem that the system had the bus topology and the star topology butno ring topology. Because of this, for example, there are conventionallyno token issuing method and token-ring communication method used toperform token ring communication in a ring-topology network constructedby the Ethernet (registered trademark).

The present invention has been made to solve the conventional problem,and it is an object of the present invention to obtain a communicationnode to perform token ring communication in the ring topologyconstructed by the Ethernet (registered trademark). It is another objectof the present invention to obtain a token issuing method in a ringcommunication system that defines issue of a token frame in the Ethernet(registered trademark)-base ring communication system. It is stillanother object of the present invention to obtain a token-ringcommunication method in the ring communication system that defines amethod of performing communications using the token passing system inthe Ethernet (registered trademark)-base ring communication system.

Means for Solving Problem

To achieve the above objects, a communication node according to anaspect of the present invention forms a communication system in which aplurality of communication nodes are connected in a ring, thecommunication nodes being one-to-one connected to each other by Ethernet(registered trademark) which is duplicated with a normal-system ringthat transmits a frame when a communication state is normal and with astandby-system ring used for transmission of a frame when thecommunication state is abnormal. The communication node includes atoken-start-right acquisition processor that issues a token-start-rightacquisition frame to acquire token start right containing specificinformation uniquely defined for the communication node after it isconfirmed that the formed ring is established, determines a prioritybased on predetermined reference using specific information for othercommunication node and the specific information for the owncommunication node upon reception of a token-start-right acquisitionframe from the other communication node, issues the token-start-rightacquisition frame at a predetermined time interval when the owncommunication node has a higher priority than the other communicationnode, and stops issuing the token-start-right acquisition frame when theown communication node has a lower priority than the other communicationnode to forward the token-start-right acquisition frame of the othercommunication node; and a token start processor that passes the tokenframe to the ring upon reception of the token-start-right acquisitionframe which is issued by the token-start-right acquisition processor andcirculates around the ring.

EFFECT OF THE INVENTION

According to the present invention, the invention is advantageous inthat it is possible to uniquely decide a token issuing station thatissues a token frame using specific information uniquely given to eachcommunication node even in a multi-vendor environment in which a ring isformed of communication nodes manufactured by different vendors.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing a rough configuration of anEthernet (registered trademark)-base ring communication system accordingto the present invention.

FIG. 2 is a block diagram schematically showing a configuration of acommunication node that forms the ring communication system of FIG. 1.

FIG. 3 is a block diagram schematically showing a functionalconfiguration of the communication node according to a first embodimentof the present invention.

FIG. 4-1 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 1).

FIG. 4-2 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 2).

FIG. 4-3 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 3).

FIG. 4-4 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 4).

FIG. 4-5 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 5).

FIG. 4-6 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 6).

FIG. 4-7 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 7).

FIG. 4-8 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 8).

FIG. 4-9 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 9).

FIG. 4-10 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 10).

FIG. 4-11 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 11).

FIG. 4-12 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 12).

FIG. 4-13 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 13).

FIG. 4-14 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 14).

FIG. 4-15 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 15).

FIG. 5 is a block diagram schematically showing a functionalconfiguration of a communication node according to a second embodimentof the present invention.

FIG. 6-1 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 1).

FIG. 6-2 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 2).

FIG. 6-3 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 3).

FIG. 6-4 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 4).

FIG. 6-5 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 5).

FIG. 6-6 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 6).

FIG. 6-7 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 7).

FIG. 6-8 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 8).

FIG. 6-9 is a diagram schematically showing an example of a procedure ofa token-start-right acquisition process in the ring communication system(part 9).

FIG. 6-10 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 10).

FIG. 6-11 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 11).

FIG. 6-12 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 12).

FIG. 6-13 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 13).

FIG. 6-14 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 14).

FIG. 6-15 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 15).

FIG. 6-16 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 16).

FIG. 6-17 is a diagram schematically showing an example of a procedureof a token-start-right acquisition process in the ring communicationsystem (part 17).

FIG. 7 is a block diagram schematically showing a functionalconfiguration of a communication node according to a third embodiment ofthe present invention.

FIG. 8-1 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 1).

FIG. 8-2 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 2).

FIG. 8-3 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 3).

FIG. 8-4 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 4).

FIG. 8-5 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 5).

FIG. 9-1 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 1).

FIG. 9-2 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 2).

FIG. 9-3 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 3).

FIG. 10-1 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 1).

FIG. 10-2 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 2).

FIG. 11-1 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 1).

FIG. 11-2 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 2).

FIG. 11-3 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 3).

FIG. 11-4 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 4).

FIG. 11-5 is a diagram showing an example of a communication processingprocedure using the token passing system in the ring communicationsystem (part 5).

FIG. 12 is a block diagram schematically showing a functionalconfiguration of a communication node according to a seventh embodimentof the present invention.

FIG. 13-1 is a diagram schematically showing an example of areproduction processing procedure of a token frame due to loss of atoken frame (part 1).

FIG. 13-2 is a diagram schematically showing an example of areproduction processing procedure of a token frame due to loss of atoken frame (part 2).

FIG. 13-3 is a diagram schematically showing an example of areproduction processing procedure of a token frame due to loss of atoken frame (part 3).

EXPLANATIONS OF LETTERS OR NUMERALS

-   10, 10-1 to 10-4 communication node-   11, 11-1 to 11-4 A port-   12, 12-1 to 12-4 B port-   17, 17-1 to 17-4 communication processor-   21 token-start-right acquisition processor-   22 token start processor-   31 frame monitor unit-   41 communication-right acquisition processor-   42 logical-ring-status control unit-   43 data-frame communication processor

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Preferred embodiments of the communication node, and the token issuingmethod and the token-ring communication method in the ring communicationsystem according to the present invention are explained in detail belowwith reference to the accompanying drawings. The present invention is byno means limited by these embodiments. In the following, the overview ofthe configuration of the present invention common to the embodiments isexplained, and thereafter, each of the embodiments is explained.

FIG. 1 is a diagram schematically showing a rough configuration of anEthernet (registered trademark)-base ring communication system accordingto the present invention. The ring communication system is constructedby connecting a plurality of communication nodes (communication devices,described as nodes in the figure) 10-1 to 10-4 in the shape of a ring,the communication nodes being one-to-one connected to each other by theEthernet (registered trademark). Here, an Ethernet (registeredtrademark) cable connecting between the communication nodes 10-1 to 10-4is physically duplicated with two rings of a normal-system ring 1,indicated by solid line in the figure, that carries a frame in theclockwise in the ring communication system, and of a standby-system ring2, indicated by dotted line, that carries a frame in thecounterclockwise. The normal-system ring 1 is a ring used when thecommunication nodes 10-1 to 10-4 and the cable that form the ringcommunication system are in the normal state. The standby-system ring 2is a ring used to separate, when abnormality occurs in any one of thecommunication nodes 10-1 to 10-4 and the cable forming the ringcommunication system, an abnormal portion from the system by a loop backprocess, which is explained later.

FIG. 2 is a block diagram schematically showing a configuration of anarbitrary communication node 10 in the ring communication system ofFIG. 1. The communication node 10 includes two ports 11 and 14 forconnecting an Ethernet (registered trademark) cable to neighboringcommunication nodes, and a communication processor 17 that processesframes received from the ports 11 and 14, and establishes a channelbetween other communication nodes.

The ports include two ports: A port (Port A in the figure) 11 and B port(Port B in the FIG. 14. The A port 11 includes a normal-system inputunit 12 that receives a frame through the normal-system ring 1 and astandby-system output unit 13 that transmits a frame to thestandby-system ring 2. The B port 14 includes a normal-system outputunit 16 that transmits a frame to the normal-system ring 1 and astandby-system input unit 15 that receives a frame through thestandby-system ring 2. It is noted that the A port 11 corresponds to“first port” in claims and the B port 14 corresponds to “second port”therein.

The communication processor 17 reads the frame which is input throughthe normal-system ring 1 and received by the normal-system input unit ofthe A port 11, and transmits the frame from the normal-system outputunit of the B port 14 to the normal-system ring 1 after a predeterminedprocess is performed thereon if necessary. Meanwhile, the communicationprocessor 17 does not read the frame which is input through thestandby-system ring 2 and received by the standby-system input unit ofthe B port 14, and transmits the frame as it is to the standby-systemoutput unit of the A port 11. More specifically, the communicationprocessor 17 performs a predetermined process only on the frame to beoutput from the B port 14 if necessary in the normal state, but does notperform any process on the frame, to be passed from the B port 14 to theA port 11 in the communication node.

When such an Ethernet (registered trademark)-base ring communicationsystem is constructed, each of the communication nodes 10-1 to 10-4 inthis system performs a ring-establishment check process to check whetherthe network to which each node belongs forms a ring-shaped channel.After the ring-establishment check process is finished, the respectivecommunication nodes 10-1 to 10-4 that form the system transmit stationinformation for the respective own communication nodes required tocreate configuration information of the network so as to be mutuallydistributed, and perform the process of creating network configurationinformation containing a positional relationship of the communicationnodes 10-1 to 10-4 and the number of communication nodes 10-1 to 10-4that form the network. This allows such a state that normalcommunications can be performed in the Ethernet (registeredtrademark)-base ring communication system. The following embodiments arebased on processes performed in the network in which thering-establishment check process and thenetwork-configuration-information creation process are finished.Further, the following embodiments are based on the Ethernet (registeredtrademark)-base ring communication system which performs datacommunication using the token passing system.

That is the overview of the Ethernet (registered trademark)-base ringcommunication system common to the embodiments. The respectiveembodiments will be explained below based on the content. It is notedthat the communication nodes 10-1, 10-2, 10-3, and 10-4 are described as#1 station, #2 station, #3 station, and #4 station, respectively, in thefollowing explanation.

For simplification of explanation, the present specification explains acase as an example where the ring communication system is formed of thefour communication nodes 10-1 to 10-4, however, the followingembodiments of the present invention can be applied to a case in whichmore than two communication nodes are connected in a ring using theEthernet (registered trademark).

First Embodiment

The first embodiment explains a token issuing method of deciding whichof the communication nodes issues a token frame used to perform tokenring communication after the ring-establishment check process and thenetwork-configuration-information creation process are finished in theEthernet (registered trademark)-base ring communication system.

FIG. 3 is a block diagram schematically showing a functionalconfiguration of the communication node according to the firstembodiment. The communication processor 17 of the communication node 10according to the first embodiment includes a token-start-rightacquisition processor 21 and a token start processor 22. It is notedthat the same numerals are assigned to the same components as these inthe explanation, and explanation thereof is omitted.

The token-start-right acquisition processor 21 performs a process foracquiring token start right to issue a token frame after thering-establishment check process and thenetwork-configuration-information creation process are finished. Thefirst embodiment explains a case where the token start right is given toa communication node added with specific information having a smallestvalue among the communication nodes that form the network, by usingunique specific information (no overlap occurs) in the world such as MAC(Media Access Control) address.

In this case, the token-start-right acquisition processor 21 sends out atoken-start-right acquisition frame in which the specific informationfor the own communication node is embedded at a predetermined timeinterval after the ring-establishment check process and thenetwork-configuration-information creation process are finished.Further, the token-start-right acquisition processor 21 comparesspecific information within a token-start-right acquisition framereceived from other communication node with the specific information forthe own communication node, continuously sends out the token-start-rightacquisition frame when the value of the specific information for the owncommunication node is smaller than the other, and discards thetoken-start-right acquisition frame as the object to be compared. If thevalue of the specific information for the own communication node isgreater than the other, the token-start-right acquisition processor 21stops sending out the token-start-right acquisition frame, and sends outthe token-start-right acquisition frame as the object to be compared.When sending of the token-start-right acquisition frame of the owncommunication node is stopped, it is determined that the communicationnode cannot acquire the token start right. Furthermore, if thetoken-start-right acquisition frame of the own communication node isreturned, this means that the token start right is acquired, and thusthe token-start-right acquisition processor 21 stops sending thetoken-start-right acquisition frame.

When the token start right is acquired, the token start processor 22sends out a token-start notification frame indicating the start ofsending a token frame to all the communication nodes on the network(ring) at a predetermined time interval. When the token-startnotification frame sent by itself circulates around the ring and isreturned, the token start processor 22 discards the token-startnotification frame, stops sending the token-start notification frame,and sends out a token frame for performing communication using the tokenpassing system.

FIG. 4-1 to FIG. 4-15 are diagrams schematically showing an example of aprocedure of the token-start-right acquisition process in the ringcommunication system. First, as shown in FIG. 4-1, upon finishing thering-establishment check process and thenetwork-configuration-information creation process, thetoken-start-right acquisition processors 21 of communication processors17-1 to 17-4 in the stations (#1 station to #4 station) 10-1 to 10-4send out first token-start-right acquisition frames 301-1 to 304-1respectively, each in which specific information for each station isembedded, at a predetermined time interval. Now, assume that the firsttoken-start-right acquisition frame 301-1 sent from the #1 station 10-1is lost due to some reason on the transmission channel between the #1station 10-1 and the #2 station 10-2.

Next, as shown in FIG. 4-2, when the communication node which has sentout the token-start-right acquisition frame receives a token-start-rightacquisition frame sent from other station, the token-start-rightacquisition processor 21 of the communication processor 17 performs amagnitude comparison between the specific information for the owncommunication node and the specific information for the sourcecommunication node in the received token-start-right acquisition frame.It is assumed in the example that pieces of the specific information forthe stations have such a magnitude relation that #1 station<#2station<#3 station<#4 station.

The token-start-right acquisition processors 21 of the communicationprocessors 17-3 and 17-4 in the #3 station 10-3 and the #4 station 10-4respectively receive the token-start-right acquisition frames sent fromthe communication nodes each with the specific information having avalue smaller than each specific information for the respective ownstations, forward received first token-start-right acquisition frames302-1 and 303-1, respectively, and stop transmitting thetoken-start-right acquisition frames from the own stations. Namely, boththe #3 station 10-3 and #4 station 10-4 cannot acquire the token startright, which means that both of those stations are “defeated”.

The token-start-right acquisition processor 21 of the communicationprocessor 17-1 in the #1 station 10-1 receives the token-start-rightacquisition frame sent from the communication node with the specificinformation having a value greater than that of the specific informationfor the own station, discards the received first token-start-rightacquisition frame 304-1 issued by the #4 station 10-4, and continues thetransmission process of the token-start-right acquisition frame from theown station.

The #2 station 10-2 which does not receive the first token-start-rightacquisition frame 301-1 having been issued by the #1 station 10-1 andbeing lost on the transmission channel cannot perform the magnitudecomparison between the pieces of the specific information, and does nottherefore perform any process.

Next, as shown in FIG. 4-3, the communication node which is not defeatedon the network again sends out the token-start-right acquisition frameafter a predetermined time passes, while the communication node which isdefeated forwards the received token-start-right acquisition frame ofother communication node. Here, the #1 station 10-1 and the #2 station10-2 belong to the communication node which is not defeated, andtherefore send out second token-start-right acquisition frames 301-2 and302-2, respectively. Meanwhile, the #3 station 10-3 and the #4 station10-4 belong to the communication node which is defeated, and thereforeforward the first token-start-right acquisition frames 302-1 and 303-1respectively which are issued by the #2 station 10-2 and the #3 station10-3, respectively.

Next, as shown in FIG. 4-4, each of the communication nodes receives thenext token-start-right acquisition frame and performs the magnitudecomparison between the pieces of the specific information as shown inFIG. 4-2. Here, the #2 station 10-2 newly enters into the defeatedstate. Consequently, as shown in FIG. 4-5, the #1 station 10-1 discardsthe first token-start-right acquisition frame 303-1 issued by thereceived #3 station 10-3, and sends out a third token-start-rightacquisition frame 301-3, while the #2 station 10-2, the #3 station 10-3,and the #4 station 10-4 respectively forward the secondtoken-start-right acquisition frame 301-2, the second token-start-rightacquisition frame 302-2, and the first token-start-right acquisitionframe 302-1 issued by the #1 station 10-1, the #2 station 10-2, and the#2 station 10-2, respectively.

Here, the token-start-right acquisition frame is successively sent outat a predetermined time interval, and thus even if the token-start-rightacquisition frame is incidentally lost due to some cause, the subsequenttoken-start-right acquisition frame circulates around the ring. As aresult, the #2 station 10-2 which cannot previously receive the firsttoken-start-right acquisition frame 301-1 issued by the #1 station 10-1also receives the token-start-right acquisition frame 301-2 issued bythe #1 station 10-1 afterward, so that the #2 station 10-2 can performthe magnitude comparison between the specific information for the owncommunication node and the specific information for the sourcecommunication node of the token-start-right acquisition frame.

The communication node (#3 station 10-3, #4 station 10-4) that stopstransmission of the token-start-right acquisition frame performs themagnitude comparison between the specific information for the ownstation and the specific information for the source station of thetoken-start-right acquisition frame each time the communication nodereceives the token-start-right acquisition frame sent from othercommunication node, and determines whether the receivedtoken-start-right acquisition frame is discarded or forwarded.

Similarly, as shown in FIG. 4-6 to FIG. 4-9, each station performs themagnitude comparison between the specific information for the ownstation and the specific information for the source station of thereceived token-start-right acquisition frame each time thetoken-start-right acquisition frame circulates to be received by eachcommunication node. The #2 station 10-2, the #3 station 10-3, and the #4station 10-4, which receive the token-start-right acquisition frameseach with the specific information having a value smaller than thespecific information for the own stations, forward the token-start-rightacquisition frames, respectively, while the #1 station 10-1 whichreceives the token-start-right acquisition frame with the specificinformation having the value greater than the specific information forthe own station discards the token-start-right acquisition frame andissues a new token-start-right acquisition frame. In other words, thecommunication nodes that send out the token-start-right acquisitionframes are limited only to the communication node (#1 station 10-1) withthe specific information having the smallest value in association withcirculation of the token-start-right acquisition frames around the ring.

Thereafter, as shown in FIG. 4-10, the token-start-right acquisitionprocessor 21 of the communication processor 17-1 in the #1 station 10-1with the specific information having the smallest value receives thesecond token-start-right acquisition frame 301-2 issued by the ownstation, and stops sending the token-start-right acquisition frame atthe time of reception thereof and thereafter. Further, by acquiring thetoken-start-right acquisition frame 301-2 issued by the own station, the#1 station 10-1 becomes a communication node which has acquired (won)the token start right, and becomes a token issuing station in thesubsequent processes.

Next, as shown in FIG. 4-11, the token start processor 22 of thecommunication processor 17-1 in the #1 station 10-1 which has acquiredthe token start right starts to send out a token-start notificationframe 311-1 at a predetermined time interval. Thereafter, as shown inFIG. 4-12 to FIG. 4-14, the communication nodes (#2 station 10-2, #3station 10-3) that receive token-start notification frames 311-1 to311-2 forward the token-start notification frames 311-1 to 311-2respectively, and are also in the standby state for token passing. The#1 station 10-1 discards the token-start-right acquisition frame issuedby itself.

Thereafter, as shown in FIG. 4-15, the token start processor 22 of thecommunication processor 17-1 in the #1 station 10-1, which sends out thetoken-start notification frame, confirms that all the token-start-rightacquisition frames on the ring are eliminated (discarded) by the factthat the token-start notification frame 311-1 circulates around the ringand returns to the own station, and starts token passing. With theseprocesses, the token issuing method in the Ethernet (registeredtrademark)-base ring communication system is finished.

It is noted that the explanation is provided only as an example, andthus, for example, the token start right may be provided to thecommunication node given with the specific information having thegreatest value among the communication nodes 10-1 to 10-4 that form thenetwork.

The reason why the #1 station 10-1 being the token issuing station inthe above explanation does not immediately output the token but outputsthe token-start notification frame 311-1 will be explained below. Eachof the communication nodes 10-1 to 10-4 incorporates therein a framemonitoring function (not shown) that monitors a frame on the network asshown in the following embodiment. If a timeout occurs, the framemonitoring function determines that the token frame is lost, and startsto transmit the token-start-right acquisition frame. At this time, anycommunication node other than the communication node 10 that issues thetoken-start-right acquisition frame receives the token-start-rightacquisition frame, and the reception causes the state to be switchedfrom a normal communication state (token passing state) to a state ofthe token-start-right acquisition process, and a token issuing stationis again decided similarly to the process. Here, if the communicationnode 10 cannot acquire the token start right, which is defeated, in theprocess of deciding the token issuing station without issuing thetoken-start notification frame and if the state is immediately changedto be ready for token passing, the communication node 10 may receive atoken-start-right acquisition frame issued by other communication node10 if the process of deciding the token issuing station is not completedor the token issuing station is not yet decided, which causes the stateto be switched to the state of the token-start-right acquisitionprocess. In this case, the defeated communication node 10 starts againto send out another token-start-right acquisition frame, and this causesthe process of deciding the token issuing station not to be settled. Toprevent such situations, it is configured to set so that the defeatedcommunication node 10 is not switched to the token passing state in themiddle of the process of deciding the token issuing station but to beready for token passing state after a token-start notification frame 311is received.

The first embodiment is advantageous that the token issuing station thatissues a token frame is uniquely decided based on the size of thespecific information uniquely added to the communication node 10 even ina multi-vendor environment in which a ring is formed of thecommunication nodes 10 manufactured by different vendors. Using a MACaddress as specific information does not cause overlap to occur, unlikethe specific information set by a user, and thus the embodiment also hasan effect that one token issuing station is always uniquely decided.

Further, each communication node 10 is configured to issue thetoken-start-right acquisition frame at a predetermined time intervaluntil it is determined that the token start right cannot be acquired.Thus, this configuration has also an effect that determination onacquisition of the token start right can be made using thetoken-start-right acquisition frame issued afterward even if thetoken-start-right acquisition frame is lost due to some cause on thenetwork. It has also an effect that there is no unnecessary frame on thenetwork, which enables prevention of false recognition of the receivedframe.

Second Embodiment

The second embodiment explains a token issue process when the tokenframe is lost caused by any undefined factor.

FIG. 5 is a block diagram schematically showing a functionalconfiguration of a communication node according to the secondembodiment. The communication processor 17 of the communication nodeaccording to the second embodiment further includes a frame monitor unit31. The frame monitor unit 31 monitors frames passing around the ringwhen the ring is in a normal communication state, and determines thatthe token frame is lost if a state in which the token frame and otherframes do not pass around the ring continues for a predetermined time.

When it is determined by the frame monitor unit 31 that the token frameis lost, the token-start-right acquisition processor 21 starts to sendout a token-start-right acquisition frame. However, if the communicationnode in the token passing state receives a token-start-right acquisitionframe sent from other communication node, the token-start-rightacquisition processor 21 discards the received token-start-rightacquisition frame only when the value of the specific information forthe source communication node of the token-start-right acquisition frameis greater than that of the specific information for the owncommunication node, and starts to send out a token-start-rightacquisition frame from the own communication node. It is noted that therest of the configuration is the same as the explanation and the samenumerals are assigned to those the same as the components in theexplanation, and thus explanation thereof is omitted.

FIG. 6-1 to FIG. 6-17 are diagrams schematically showing an example of aprocedure of a token-start-right acquisition process in the ringcommunication system. First, it is assumed that a token frame is lostcaused by any undefined factor in the normal communication state of thetoken ring system. Thereafter, as shown in FIG. 6-1, the frame monitorunit 31 of the communication processor 17-3 in the #3 station 10-3 firstdetects the loss of the token frame, and the token-start-rightacquisition processor 21 starts to send out a token-start-rightacquisition frame 303-1 at a predetermined time interval.

Thereafter, as shown in FIG. 6-2, the #4 station 10-4 during tokenpassing receives the token-start-right acquisition frame 303-1 issued bythe #3 station 10-3, and the token-start-right acquisition processor 21of the communication processor 17-4 performs the magnitude comparisonbetween the specific information for the own station and the specificinformation for the source communication node (#3 station 10-3) of thetoken-start-right acquisition frame 303-1. Similarly to the firstembodiment, it is also assumed that the pieces of the specificinformation for the stations have such a magnitude relation as #1station<#2 station<#3 station<#4 station. Consequently, the #4 station10-4 receives the token-start-right acquisition frame sent from thecommunication node with the specific information having a value smallerthan the specific information for the own station, and thus the #4station 10-4 cannot obtain the token start right, which is defeated. Asshown in FIG. 6-3, the #4 station 10-4 stops the token passing, andforwards the received token-start-right acquisition frame 303-1 withoutany change given thereto.

Meanwhile, as shown in FIG. 6-4 to FIG. 6-5, the token-start-rightacquisition frame 303-1 next reaches the #1 station 10-1. Similarly tothe above, the #1 station 10-1 performs the magnitude comparison betweenthe specific information for the source communication node (#3 station10-3) of the token-start-right acquisition frame and the specificinformation for the own station. The token-start-right acquisitionprocessor 21 of the communication processor 17-1 in the #1 station 10-1receives the token-start-right acquisition frame sent from thecommunication node with the specific information having the valuegreater than the specific information for the own station, stops thetoken passing, discards the received token-start-right acquisition frame303-1 of the #3 station 10-3, and starts to send out a token-start-rightacquisition frame 301-1 from the own station at a predetermined timeinterval. As shown in FIG. 6-6 to FIG. 6-7, the token-start-rightacquisition frames circulate, and the same process is performed in the#1 station 10-1, the #2 station 10-2, and the #4 station 10-4,respectively, each of which receives the next token-start-rightacquisition frame. During the process, the #2 station 10-2 that receivesthe token-start-right acquisition frame 301-1 with the specificinformation having a value smaller than the specific information for theown station cannot acquire the token start right, which is defeated.

Thereafter, as shown in FIG. 6-8 to FIG. 6-9, when the #3 station 10-3that originally sends out the token-start-right acquisition frame 303-1receives the token-start-right acquisition frame 301-1 sent from the #1station 10-1, the token-start-right acquisition processor 21 of thecommunication processor 17-3 performs the magnitude comparison betweenthe specific information for the own station and the specificinformation for the source communication node (#1 station 10-1) in thetoken-start-right acquisition frame 301-1. Here, the #3 station 10-3receives the token-start-right acquisition frame 301-1 sent from the #1station 10-1 with the specific information having the value smaller thanthe specific information for the own station, and thus the #3 station10-3 cannot obtain the token start right, which is defeated. Then, the#3 station 10-3 forwards the received token-start-right acquisitionframe 301-1 of the #1 station 10-1, and stops the process of sending thetoken-start-right acquisition frame from the own station.

In this case also, the communication node (#1 station 10-1) thatreceives the token-start-right acquisition frame sent from thecommunication node with the specific information having a value greaterthan the specific information for the own station discards the receivedtoken-start-right acquisition frame, and continues transmission of thetoken-start-right acquisition frame from the own communication node.

Next, as shown in FIG. 6-10 to FIG. 6-11, the communication nodes thatsend out the token-start-right acquisition frames are limited only tothe communication node (#1 station 10-1) with the specific informationhaving the smallest value in association with circulation of thetoken-start-right acquisition frames 301-1 and 301-2 around the ring.

Thereafter, as shown in FIG. 6-12, the token-start-right acquisitionprocessor 21 of the communication processor 17-1 in the #1 station 10-1with the specific information having the smallest value first receivesthe token-start-right acquisition frame 301-1 issued by the own station,and stops sending the token-start-right acquisition frame at the time ofreception thereof and thereafter. Further, by acquiring thetoken-start-right acquisition frame 301-1 issued by the own station, the#1 station 10-1 becomes a communication node which has acquired (won)the token start right, and becomes a token issuing station in thesubsequent processes.

Next, as shown in FIG. 6-13, the token start processor 22 of thecommunication processor 17-1 in the #1 station 10-1 which has acquiredthe token start right starts to send out a token-start notificationframe 311-1 at a predetermined time interval. Thereafter, as shown inFIG. 6-14 to FIG. 6-17, the #2 station 10-2 to the #4 station 10-4 thatreceive the token-start notification frames 311-1 to 311-4 forward thetoken-start notification frames 311-1 to 311-4 respectively, and arealso in a standby state for token passing. The #1 station 10-1 discardsthe token-start-right acquisition frame 301-2 issued by itself.

Thereafter, as shown in FIG. 6-17, the token start processor 22 of thecommunication processor 17-1 in the #1 station 10-1 which sends out thetoken-start notification frames 311-1 to 311-4 confirms that all thetoken-start-right acquisition frames on the ring are eliminated(discarded) by the fact that the token-start notification frame 311-1returns to the own station, and starts token passing. With theseprocesses, the token issuing method is finished.

It is noted that the explanation is provided as an example, and thus,for example, the token start right may be provided to the communicationnode given with the specific information having the greatest value amongthe communication nodes 10-1 to 10-4 that form the network.

According to the second embodiment, it is configured to immediatelydetect the loss of the token frames of the communication nodes in allthe stations, and to switch the state of the detected communication nodefrom the token passing state to the token-start-right acquisition state,and thus, it is possible to quickly restart the token passing. Moreover,the second embodiment has an effect that there is no unnecessary frameon the ring and thus false recognition of the received frame can beprevented.

Third Embodiment

The third embodiment explains a case where communications are performedusing the token passing system in the Ethernet (registeredtrademark)-base ring communication system.

FIG. 7 is a block diagram schematically showing a functionalconfiguration of a communication node according to the third embodiment.The communication processor 17 of the communication node 10 includes acommunication-right acquisition processor 41, a logical-ring-statuscontrol unit 42, and a data-frame communication processor 43. It isnoted that the same numerals are assigned to components the same asthese in the explanation above, and explanation thereof is thereforeomitted.

When the own communication node wishes to transmit data, thecommunication-right acquisition processor 41 takes a token frame passingaround the ring to acquire communication right, and transmits atoken-receipt completion notification frame (hereinafter, “token Ackframe”) indicating acquisition of the token frame to the communicationnode that releases the token frame. The communication-right acquisitionprocessor 41 releases the token frame when the data-frame communicationprocessor 43 finishes transmission of the data frame.

The logical-ring-status control unit 42 controls switching between astatus in a transmission mode of logically disconnecting the ring withinthe own communication node and discarding all the frames received by theown communication node without forwarding them when thecommunication-right acquisition processor 41 acquires the communicationright, and a status in a repeat mode of finishing the disconnection ofthe logical ring and forwarding all the frames received by the owncommunication node when the token Ack frame is received from othercommunication node.

The data-frame communication processor 43 that acquires thecommunication right transmits the data wished to be transmitted as adata frame and the own communication node transmits the data. Thestructure of the data frame to be communicated at the time is the sameas the ordinary Ethernet (registered trademark) frame which contains adestination MAC address and a source MAC address. The data-framecommunication processor 43 performs a process of receiving a data frameaddressed to the own communication node from other communication node.It is noted that when the own communication node is in the transmissionmode, the data-frame communication processor 43 discards all thereceived frames without forwarding them and forwards all the receivedframes when the own communication node is in the repeat mode.

FIG. 8-1 to FIG. 8-5 are diagrams showing an example of a communicationprocessing procedure using the token passing system in the Ethernet(registered trademark)-base ring communication system. Here, a case inwhich a data frame transmitted as a communication message is addressedto all communication nodes on the ring through broadcast is explained asan example.

First, the #1 station 10-1 that has already acquired a token frame 320is in the transmission mode in which the ring within the own station islogically disconnected by the logical-ring-status control unit 42 of thecommunication processor 17, and the data-frame communication processor43 performs sending of a communication message (hereinafter, “dataframe”) 321 and a termination process (discard process) on the dataframe 321 issued by the own station. When the sending of all the dataframes 321 is completed by the data-frame communication processor 43,the communication-right acquisition processor 41 transmits a token frame320. After the transmission of the token frame 320, the #1 station 10-1remains in the transmission mode (FIG. 8-1). It is noted that, as shownin the #2 station 10-2 to the #4 station 10-4 of FIG. 8-1, each state inwhich solid lines are extended from A ports 11-2 to 11-4 to B ports 14-2to 14-4 respectively indicates the repeat mode, while as shown in the #1station 10-1, a state in which the solid line is not extended from an Aport 11-1 to a B port 14-1 indicates the transmission mode in which thering is logically disconnected.

Next, the #2 station 10-2 that receives the token frame 320 performstermination (acquisition) of the token frame 320 in thecommunication-right acquisition processor 41 of the communicationprocessor 17-2. The communication-right acquisition processor 41receives the token frame 320 from the #1 station 10-1, and thereforetransmits a token Ack frame 331 to the #1 station 10-1 which is a tokenrelease station. The logical-ring-status control unit 42 logicallydisconnects the ring in the own station to switch to the transmissionmode. The data-frame communication processor 43 performs sending of adata frame 322 and a termination process on the data frame 322 issued bythe own station. When the sending of all the data frames 322 iscompleted by the data-frame communication processor 43, thecommunication-right acquisition processor 41 transmits the token frame320. Note that the #2 station 10-2 remains in the transmission modeafter the token frame 320 is transmitted (FIG. 8-2).

Thereafter, the frames circulate, and the #1 station 10-1 receives thedata frame 321 issued by itself. At this time, because the #1 station10-1 is in the transmission mode, the data-frame communication processor43 discards the received data frame 321 (FIG. 8-3).

Subsequently, the #1 station 10-1 receives the token Ack frame 331addressed to the own station. At this time, because the #1 station 10-1is in the transmission mode, the data-frame communication processor 43discards the received token Ack frame 331, and the logical-ring-statuscontrol unit 42 switches the status of the own station, upon receptionof the token Ack frame 331, from the transmission mode to the repeatmode in which logical disconnection of the ring is finished (FIG. 8-4).Thereafter, all the frames received from the A port 11-1 of the #1station 10-1 are forwarded (FIG. 8-5). The stations perform theprocesses shown in FIG. 8-1 to FIG. 8-5, so that communications usingthe token passing system are performed.

According to the third embodiment, it is configured to set thetransmission mode of logically disconnecting the ring within thecommunication node 10, in the communication node 10 that acquires thecommunication right, and to set the repeat mode of forwarding thereceived frame in the communication node 10 that does not acquire thecommunication right. Thus, the third embodiment has an effect that thecommunication node 10 that acquires the communication right can discardthe frame issued by the own communication node 10 without fragmentingthe frame.

It is also configured that the communication node 10 which takes a tokenframe and acquires the communication right transmits the token Ack frameto the source communication node of the token frame. Thus, the thirdembodiment has an effect that the switching from the transmission modeto the repeat mode can be performed using the token Ack frame.Consequently, it is possible to remove the frame and the token Ack frameissued by the own communication node 10 from the ring, and to preventany unnecessary frame from staying on the ring.

Fourth Embodiment

The third embodiment is configured that the communication node whichreleases the token frame and is in the transmission mode (hereinafter,“token-released communication node”) receives the token Ack frameaddressed to the own station from a next communication node whichacquires the token frame (hereinafter, “token-acquired communicationnode”), to thereby change the state from the transmission mode to therepeat mode. In this case, however, the token Ack frame sent from thetoken-acquired communication node may sometimes be lost by any cause. Inthe fourth embodiment, a communication method using the token passingsystem when the token Ack frame is lost before it reaches thetoken-released communication node will be explained below.

The functional configuration of the communication node according to thefourth embodiment is the same as that of FIG. 7 according to the thirdembodiment. In the fourth embodiment, however, the logical-ring-statuscontrol unit 42 of the communication processor 17 in FIG. 7 furtherincludes a function of changing to the repeat mode, in the transmissionmode, upon reception of the data frame transmitted by othercommunication node (token-acquired communication node) before the tokenAck frame addressed to the own communication node is received.

FIG. 9-1 to FIG. 9-3 are diagrams showing an example of a communicationprocessing procedure using the token passing system in the Ethernet(registered trademark)-base ring communication system. First, asexplained with reference to FIG. 8-1 to FIG. 8-2 of the thirdembodiment, the #2 station 10-2 sends out the data frame 321, takes thetoken frame 320 from the #1 station 10-1 that releases the token frame320, and sends the token Ack frame 331 addressed to the #1 station 10-1which is the token-released communication node and the data frame 322out on the ring.

Thereafter, the frames circulate, and the #1 station 10-1 receives thedata frame 321 issued by itself. At this time, because the #1 station10-1 is in the transmission mode, the data-frame communication processor43 discards the received data frame 321. At this time, it is assumedthat the token Ack frame 331 is lost on the ring between the #4 station10-4 and the #1 station 10-1 caused by any undefined factor (FIG. 9-1).

Thereafter, the #1 station 10-1 receives the data frame 322 issued byother station (#2 station 10-2) without receiving the token Ack frame331 addressed to the own station (FIG. 9-2). The logical-ring-statuscontrol unit 42 of the communication processor 17-1 in the #1 station10-1 detects that the data frame 322 of the other station is receivedwithout receiving the token Ack frame 331, switches the state of the ownstation from the transmission mode to the repeat mode, and finishes thelogical disconnection of the ring within the #1 station 10-1.Consequently, the data-frame communication processor 43 of thecommunication processor 17-1 in the #1 station 10-1 forwards thereceived data frame 322 sent from the #2 station 10-2 as it is, andforwards all the frames received thereafter (FIG. 9-3).

According to the fourth embodiment, even if the token Ack frame is lost,the state of the token-released communication node can be changed fromthe transmission mode to the repeat mode using the function that thedata frame arrives after the token Ack frame. As a result, the fourthembodiment has an effect that even if the token Ack frame is lost, thesubsequent frame is prevented from being carelessly discarded.

Fifth Embodiment

The fourth embodiment is configured that even if the token Ack frameaddressed to the own station is lost, the token-released communicationnode changes the state from the transmission mode to the repeat mode byreception of the data frame received after the loss. In this case,however, there is also a case in which the data frame may be lost due toany cause in addition to the token Ack frame sent from thetoken-acquired communication node. The fifth embodiment explains thecommunication method using the token passing system when the token Ackframe and the data frame issued by the token-acquired communication nodeare lost before they reach the token-released communication node.

The functional configuration of the communication node according to thefifth embodiment is the same as that of FIG. 7 according to the thirdembodiment. In the fifth embodiment, however, the logical-ring-statuscontrol unit 42 of the communication processor 17 in FIG. 7 furtherincludes a function of changing to the repeat mode, in the transmissionmode, upon reception of the data frame transmitted by othercommunication node (token-acquired communication node) before the tokenAck frame addressed to the own communication node is received, or uponreception of the token Ack frame addressed to other communication nodeissued by further another communication node before the token Ack frameaddressed to the own communication node and the data frame issued by theother communication node (token-acquired communication node) arereceived.

FIG. 10-1 to FIG. 10-2 are diagrams showing an example of acommunication processing procedure using the token passing system in theEthernet (registered trademark)-base ring communication system. First,as explained with reference to FIG. 8-1 to FIG. 8-2 of the thirdembodiment, the #2 station 10-2 sends out the data frame 321, takes thetoken frame 320 from the #1 station 10-1 that releases the token frame320, sends the token Ack frame 331 addressed to the #1 station 10-1which is the token-released communication node and the data frame 322out on the ring, and then releases the token frame 320. Thereafter, asexplained with reference to FIG. 9-1 according to the fourth embodiment,the frames circulate, and the #1 station 10-1 receives the data frame321 issued by itself, and discards the relevant data frame 321. At thistime, it is assumed that the #3 station 10-3 takes the token frame 320and the token Ack frame 331 is lost caused by any undefined factor onthe ring between the #4 station 10-4 and the #1 station 10-1.

The frames further circulates, however, it is assumed that the dataframe 322 issued by the #2 station 10-2 is also lost on the transmissionchannel between the #4 station 10-4 and the #1 station 10-1. Meanwhile,the communication-right acquisition processor 41 in the #3 station 10-3that takes the token frame 320 transmits a token Ack frame 332 addressedto the #2 station 10-2 which is a source of the token frame 320.Thereafter, the data-frame communication processor 43 of the #3 station10-3 transmits a data frame 323 (FIG. 10-1).

Thereafter, the #1 station 10-1 receives the token Ack frame 332addressed to the #2 station 10-2 issued by the #3 station 10-3 withoutreceiving the token Ack frame 331 addressed to the own station and thedata frame 322 that is supposed to be issued by other station (#2station 10-2). The logical-ring-status control unit 42 of thecommunication processor 17-1 in the #1 station 10-1 detects that thetoken Ack frame 332 addressed to the #2 station 10-2 issued by the #3station 10-3 is received without receiving the token Ack frame 331addressed to the own station and the data frame 322 issued by the #2station 10-2, switches the state of the own station from thetransmission mode to the repeat mode, and finishes the logicaldisconnection of the ring within the #1 station 10-1. Consequently, thedata-frame communication processor 43 of the communication processor17-1 in the #1 station 10-1 forwards the received token Ack frame 332addressed to the #2 station 10-2 issued by the #3 station 10-3 as it is,and forwards all the frames received thereafter (FIG. 10-2).

According to the fifth embodiment, by using the function that a dataframe (data frame) arrives after a token Ack frame and a token Ack frameaddressed to some other station issued by other communication nodearrives after the data frame, the state of the token-releasedcommunication node can be changed from the transmission mode to therepeat mode even if the token Ack frame and the data frame are lost. Asa result, the fifth embodiment has an effect that even if the token Ackframe and the data frame are lost, the subsequent frame is preventedfrom being carelessly discarded.

Sixth Embodiment

The fifth embodiment is configured that even if the token Ack frameaddressed to the own communication node and the subsequent data frameare lost, the state of the token-released communication node is changedfrom the transmission mode to the repeat mode by reception of the tokenAck frame addressed to some other communication node issued by otherstation which is received after they are lost. In addition, the sixthembodiment explains a communication method using the token passingsystem when a token Ack frame and a data frame issued by othercommunication node and addressed to some other communication node arelost and a communication node that is supposed to receive a token Ackframe addressed to the own communication node receives the token framewithout receiving the token Ack frame and the data frame.

The functional configuration of the communication node according to thesixth embodiment is the same as that of FIG. 7 according to the thirdembodiment. In the sixth embodiment, however, the communication-rightacquisition processor 41 of the communication processor 17 in FIG. 7further includes a function of taking a token frame and transmitting atoken Ack frame to a source communication node of the token frame, inthe transmission mode, when a token frame is again received withoutreceiving a data frame issued by other communication node and a tokenAck frame addressed to other communication node in addition to the tokenAck frame addressed to the own communication node. The data-framecommunication processor 43 further includes a function of againtransmitting the data frame issued by the own communication nodereceived before receiving the token Ack frame addressed to the owncommunication node.

FIG. 11-1 to FIG. 11-5 are diagrams showing an example of acommunication processing procedure using the token passing system in theEthernet (registered trademark)-base ring communication system. First,as explained with reference to FIG. 8-1 to FIG. 8-2 of the thirdembodiment, the #2 station 10-2 sends out the data frame 321, takes thetoken frame 320 from the #1 station 10-1 that releases the token frame320, sends the token Ack frame 331 addressed to the #1 station 10-1which is the token-released communication node and the data frame 322out on the ring, and then releases the token frame.

Thereafter, the frames circulate, and the #1 station 10-1 receives thedata frame 321 issued by itself. At this time, because the #1 station10-1 is in the transmission mode, the data-frame communication processor43 discards the received data frame 321. Further, at this time, it isassumed that the #3 station 10-3 takes the token frame 320 and acquiresthe communication right, and that the token Ack frame 331 addressed tothe #1 station 10-1 is lost caused by any undefined factor on the ringbetween the #4 station 10-4 and the #1 station 10-1 (FIG. 11-1).

It is further assumed that although the frames circulate, the data frame322 issued by the #2 station 10-2 and the token Ack frame 332 addressedto the #2 station 10-2 issued when the #3 station 10-3 takes the tokenframe 320 are also lost caused by any undefined factor on the ringbetween the #4 station 10-4 and the #1 station 10-1. At this time, the#3 station 10-3 sends out the data frame 323 and then releases the tokenframe 320 (FIG. 11-2).

The frames further circulate, and the #4 station 10-4 takes the tokenframe 320 and acquires the communication right. It is also assumed thatthe data frame 323 issued by the #3 station 10-3 and a token Ack frame333 addressed to the #3 station 10-3 issued when the #4 station 10-4takes the token frame 320 are also loss caused by any undefined factoron the ring between the #4 station 10-4 and the #1 station 10-1 (FIG.11-3).

Next, the #4 station 10-4 transmits a data frame 324 and releases thetoken frame 320. At this time, it is assumed that the data frame 324issued by the #4 station 10-4 is also lost caused by any undefinedfactor on the ring between the #4 station 10-4 and the #1 station 10-1(FIG. 11-4). Thereafter, the #1 station 10-1 receives the token frame320 released by the #4 station 10-4. The communication-right acquisitionprocessor 41 of the #1 station 10-1 receives the data frame 321previously issued by the own station, and then again receives the tokenframe 320 without receiving even any one of the token Ack frame 331addressed to the own communication node, the data frames 322 to 324issued by other stations, and the token Ack frames 332 and 333 addressedto other communication nodes. Thus the communication-right acquisitionprocessor 41 takes the received token frame 320 and acquires thecommunication right. Additionally, the communication-right acquisitionprocessor 41 transmits a token Ack frame 334 to the #4 station 10-4which is the token-released communication node (FIG. 11-5). Thedata-frame communication processor 43 again transmits the data frame 321transmitted in FIG. 8-1, and then releases the token frame 320. It isnoted that the logical-ring-status control unit 42 does not switch thestate because the #1 station 10-1 is already in the transmission modeupon reception of the token frame 320.

Thereafter, in the communication nodes (#3 station 10-3 and #4 station10-4) provided in the downstream side of the #2 station 10-2, if noframe is lost, the state is switched from the transmission mode to therepeat mode as explained in the fifth embodiment, using the token Ackframe 334 addressed to the #4 station 10-4 transmitted by the #1 station10-1.

According to the sixth embodiment, it is configured that when receivinga token frame without receiving a token Ack frame and a data frame, thecommunication node which is supposed to receive the token Ack frameaddressed to the own station takes the token frame and transmits thedata frame the same as that received before the token Ack frameaddressed to the own communication node is received. Thus, the sixthembodiment has an effect that the data can be reliably delivered to adestination communication node.

Seventh Embodiment

The seventh embodiment explains a regeneration process of a token framewhen the token frame is lost caused by any undefined factor duringcommunication using the token passing system.

FIG. 12 is a block diagram schematically showing a functionalconfiguration of a communication node according to the seventhembodiment. The communication node 10 is configured to combine theconfiguration of FIG. 5 according to the second embodiment with that ofFIG. 7 according to the third embodiment. Specifically, thecommunication processor 17 of the communication node 10 includes thetoken-start-right acquisition processor 21 that performs the acquisitionprocess of the token start right, the token start processor 22 thatperforms notification that a communication node acquiring the tokenstart right starts communication using the token passing system to allthe communication nodes on the ring, the frame monitor unit 31 thatmonitors the token frame, the token Ack frame, and the data framepassing around the ring, the communication-right acquisition processor41 that performs the process of acquiring communication right in thestate of starting the communication using the token passing system, thelogical-ring-status control unit 42 that controls switching between astatus of logically disconnecting the ring within the communication nodeand a status of logically connecting the ring, and the data-framecommunication processor 43 that performs a communication process of thedata frame.

Here, the frame monitor unit 31 monitors all the frames including thetoken frame, the token Ack frame, and the data frame which pass aroundthe ring, and detects that the token may be lost if the frames do notpass around the ring for more than a predetermined time.

FIG. 13-1 to FIG. 13-4 are diagrams schematically showing an example ofa reproduction processing procedure of a token frame due to loss of atoken frame. It is noted that black circles added to the A ports 11-1 to11-4 in these figures represent frame monitor units 31-1 to 31-4provided in the communication processors 17-1 to 17-4, respectively.First, the #1 station 10-1 takes a token frame 320 and transmits a dataframe 321, and then releases the token frame 320. Thereafter, it isassumed that the token frame 320 is lost on the ring between the #1station 10-1 and the #2 station 10-2 caused by any undefined factor(FIG. 13-1). At this time, only the #1 station 10-1 that sends out thedata frame 321 is in the transmission mode, and the #2 station 10-2 tothe #4 station 10-4 are in the repeat mode.

When the data frame 321 issued by the #1 station 10-1 circulates andagain returns to the #1 station 10-1 to be received thereby, the #1station 10-1 discards the received data frame 321 because it is in thetransmission mode (FIG. 13-2). A frame monitor unit 31-2 of the #2station 10-2 detects that no frame is received more than a predeterminedtime after the data frame 321 is received and forwarded the last time(the frames do not pass around the ring) (FIG. 13-3). Namely, the framemonitor unit 31-2 detects that the token frame 320 is lost.Consequently, the token-start-right acquisition processor 21 of thecommunication processor 17-2 in the #2 station 10-2 performs the processof acquiring the token start right as explained in the secondembodiment, and starts the process of regenerating the token frame 320(FIG. 13-4). This figure shows a state in which the #2 station 10-2sends out the token-start-right acquisition frame 302-1 at apredetermined time interval.

In FIG. 13-3, the reason why the #2 station 10-2 first detects the lossof the token frame 320 is because the #2 station 10-2 is the nearest toa location where the token frame 320 is lost, among the communicationnodes which are located in the downstream side of the location where thetoken frame 320 is lost. In this case, it is assumed that a time (timervalue) used to determine the loss of the token frame 320 is constant inall the communication nodes 10-1 to 10-4 on the ring.

According to the seventh embodiment, even when the token frame is lostduring communication using the token passing system, the loss can bedetected, and thus the token frame can quickly be regenerated. As aresult, the seventh embodiment has an effect that the token frame can beautomatically recovered from its loss.

INDUSTRIAL APPLICABILITY

As explained above, the Ethernet (registered trademark)-base ringcommunication system according to the present invention is useful for anetwork formed of a plurality of communication nodes.

1. A communication node in a communication system in which a pluralityof communication nodes are connected by Ethernet (registered trademark)in a ring shape, the communication node comprising: acommunication-right acquisition processor that, when receiving a tokenframe and acquiring a communication right, transmits a token-receiptcompletion notification frame addressed to a source communication nodeof the token frame, and releases the token frame when the a data frametransmission is finished; a logical-ring-status control unit thatswitches between a transmission mode of disconnecting a logicalconnection within the own communication node upon acquisition of thecommunication right, and a repeat mode of finishing the disconnection ofthe logical connection within the own communication node upon receptionof a token-receipt completion notification frame addressed to the owncommunication node; and a data-frame communication processor thattransmits/receives a data frame, wherein the data-frame communicationprocessor discards all received frames when the communication node is inthe transmission mode, and forwards a received frame when thecommunication node is in the repeat mode.
 2. The communication nodeaccording to claim 1, wherein the logical-ring-status control unitswitches the status of the own communication node to the repeat modeupon reception of a token-receipt completion notification frameaddressed to other communication node without receiving thetoken-receipt completion notification frame addressed to the owncommunication node.
 3. The communication node according to claim 2,wherein the data-frame communication processor forwards a frame receivedafter receiving the token-receipt completion notification frameaddressed to the other communication node.
 4. A token-ring communicationmethod in a communication system in which a plurality of communicationnodes are connected by Ethernet (registered trademark) in a ring shapeand communication is performed using a token passing system, thetoken-ring communication method comprising: a communication-rightacquisition step of receiving a token frame to acquire a communicationright, and transmitting a token-receipt completion notification frameaddressed to a source communication node of the token frame; atransmission-mode switch step of disconnecting a logical connectionwithin the own communication node upon acquisition of the communicationright, and switching the own communication node to a transmission mode;a data-frame transmission step of transmitting a data frame to acommunication node of a desired destination; a token-frame release stepof releasing the token frame when transmission of a data frame to betransmitted is finished; and a repeat-mode switch step of discarding allreceived frames before a token-receipt completion notification frameaddressed to the own communication node is received, finishing thedisconnection of the logical connection within the own communicationnode when the token-receipt completion notification frame addressed tothe own communication node is received, switching the own communicationnode to a repeat mode, and forwarding a frame received after theswitching.
 5. The token-ring communication method according to claim 4,wherein the repeat-mode switch step includes switching the status of theown communication node to the repeat mode when a token-receiptcompletion notification frame addressed to other communication node isreceived without receiving the token-receipt completion notificationframe addressed to the own communication node.
 6. The token-ringcommunication method according to claim 5, wherein the repeat-modeswitch step further includes forwarding a frame received after receivingthe token-receipt completion notification frame addressed to the othercommunication node.